MORPHOSTRUCTURES IN MOMCHILGRAD DEPRESSION

Geogiev V. et al. MORPHOSTRUCTURES IN MOMCHILCRAD …
Минно-геоложки университет “Св. Иван Рилски”
Годишник, том 47, свитък I, Геология и геофизика, София, 2004, стр. 69-73
MORPHOSTRUCTURES IN MOMCHILGRAD DEPRESSION (Еastern Rhodopes)
V. Georgiev 1, R. Marinova 2, G. Jelev 3
1, 2 Geological
3 Space
Institute, Bulgarian Academy of Sciences, 1113 Sofia, e-mail: vladogeo@geology.bas.bg
Research Institute, Bulgarian Academy of Sciences, 1113 Sofia, e-mail: gjelev@space.bas.bg
ABSTRACT. The Late Alpine Momchilgrad Depression is located between the Central Rhodopes and the Byala Reka metamorphic core complexes (domes) in the
eastern periphery of the Rhodopes massif. Several volcanic edifices of intermediate composition and many acid extrusions have been mapped in the confines of the
Depression. These relatively young structures are directly reflected in the modern morphostructural plan and can be easily detected on aerial photographs and space
images. Morphostructural and morphometric studies and the GIS potentialities of the relief outline the domes of the metamorphic core complexes as positive arch
morphostructures. Between them, the Momchilgrad Depression forms a negative structure contoured by well-manifested morpholineaments. The Paleogene volcanic
cones and extrusions are registered as second-order positive morphostructures in the Depression. These features are very well expressed on space images and are
interpreted as photoanomalies of linear, arch, or circular pattern.
Key words: morphostructures, Momchilgrad Depression, Eastern Rhodopes, remote sensing, GIS.
МОРФОСТРУКТУРИ В МОМЧИЛГРАДСКАТА ДЕПРЕСИЯ (Източни Родопи)
В. Георгиев 1, Р. Маринова 2, Г. Желев 3
Геологически институт, БАН, 1113 София, е-mail: vladogeo@geology.bas.bg
Институт за космически изследвания, БАН, 1113 София, е-mail: gjelev@space.bas.bg
РЕЗЮМЕ. Късноалпийската Момчилградска депресия се разполага между Централнородопския и Белоречкия ядрени комплекси (куполи) в източния фланг
на Родопския масив. В нея са локализирани няколко среднокисели вулкански постройки и редица кисели екструзии. Тези сравнително млади структури
намират пряко отражение в съвременния морфоструктурен план и се дешифрират по аерофото снимки. Въз основа на морфоструктурни и морфометрични
изследвания в релефа добре се очертават куполите на ядрените комплекси като положителни сводови морфоструктури. Между тях като отрицателна
структура се очертава Момчилградската депресия, отделена с много добре изразени морфолинеаменти. В пределите на депресията, като положителни
морфоструктури от втори ранг, изпъкват палеогенските вулкански конуси и екструзии.
periphery of the Depression and its framework (Georgiev,
Milovanov, 2003).
Trachyrhyodacite to trachyrhyolite and latite dikes from the
Pcheloyad dike complex occur in the southern part of the
Depression and its frame.
Geological setting
The Momchilgrad Depression is located between the Central
Rhodopes (to NW), the Byala Reka and the Kessibir (to SE)
metamorphic core complexes (domes) of the Rhodope massif,
and the Kurdzhali block to the north (Georgiev, 2004).
The basement and framework of the Depression comprise
pre-Paleogene metamorphic rocks (various gneisses, marbles,
amphibolites, serpentinized ultrabasites).
The Kurdzhali block, occupying an intermediate hypsometric
level between the core complexes and the Momchilgrad
Depression, is composed mainly of Eocene sediments and
Lower Oligocene acid pyroclastic rocks.
The basal parts of the Depression are build up of PaleoceneOligocene terrigenous sediments and reefal limestones.
In the end of the Priabonian and during the Oligocene formed
the Iran Tepe, Sveti Iliya, Bivolyane, Dambaluk, and Zvezdel
volcanoes (Fig.1). They are composed of the materials of the
Putochara intermediate subgroup and the Zdravets acid
subgroup pertaining to the Dambala magmatic group. The
Nanovitsa caldera, located between them, is filled with
products of the Sveti Iliya trachyrhyodacite and the Ravena
rhyolite complex.
Extrusives from the Perperek trachyrhyolite and the Ustren
rhyolite complex are exposed along the northern and western
Methods
To highlight the morphostructure of the Momchilgrad
Depression and its framework, aerial photographs and space
images (LandSat TM) in scale 1:20,000 and 1:100,000 were
deciphered and an aerophototectonic map was compiled
(Fig.2). A morphostructural map of the tectonoisohypses was
constructed, too (Fig. 3).
In the process of deciphering of aerial photographs and
space images, both direct and indirect methods for
interpretation of lineaments and ring structures were used.
Nowadays, the quick development of computer engineering
and the integration of data bases into GIS enables to use
interactive methods in georeferencing, processing,
deciphering, and interpretation of modern remote sensing data,
as well as to use this data in complex with ground-based data.
The spatial juxtaposing of complex data allows to separate
surface and in-depth lineament manifestations (Кац Я. и др.
1988).
ГОДИШНИК на Минно-геоложкия университет “Св. Иван Рилски”, том 47 (2004), свитък I, ГЕОЛОГИЯ И ГЕОФИЗИКА
69
Geogiev V. et al. MORPHOSTRUCTURES IN MOMCHILCRAD …
The generalized outlook of the Momchilgrad Depression, its
constituent higher-order morphostructures, and its
metamorphic framework are reflected on the tectonoisohypse
map. The area structures manifested directly in the modern
relief are fixed by the circular form of the tectonoisohypses
outlining positive morphostructures. Furthermore, the modern
dynamics of these morphostructures is outlined by the
centrifugal configuration of the river-gorge network. The linear
tectonic elements (morpholineaments) are manifested either by
congestion of the rectilinear tectonoisohypses or by their kneelikebendings. The morpholineaments are also outlined by the
rectilinear segments of the river valleys.
Fig. 1. Geologic-structural map of the Momchilgrad Depression. 1– fault; 2 – volcanic cone or extrusive; 3 – Neogene-Quaternary deposits; 4 – acid tuffs
(а) and effusives (b); 5 – intermediate tuffs (а), effusives (b) and intrusions (c); 6 – Paleogene sediments; 7 – pre-Paleogene basement; ZV- Zvezdel
volcano; DV- Dambaluk volcano; BV- Bibolyane volcano; SIV- Svety Iliya; ITV- Iran Tepe volcano; CRD- Central Rhodopes dome; BRD- Byala Reka
dome;KSD- Kessibir dome
Momchilgrad Depression feature a hypsometric level of 500600 m.
The inner structure of these first-order positive
morphostructures is complicated by a number of second-order
morpholineaments. Extensional stresses in the crestal and
peripheral parts of the domes produced superimposed
negative structures that are filled with continental and marine
sediments.
Along the border between the arch-block morphostructures,
Neogene-Quaternary valley extensions are formed, often
featuring asymmetric structure.
Morphostructures of the metamorphic
framework
In the beginning of Paleogene, the factor accounting for relief
formation was arch formation, related with the formation of
core metamorphic complexes in connection with extension
processes (Ivanov, 2000). On the modern morphostructural
plan, the first-order tectonic structures are well manifested –
the Central Rhodopes, the Byala Reka, and the Kessibir core
complexes (domes). These form morphoarches, which feature
a high and strongly segmented relief. To the north of the Byala
Reka morphoarch, a second-order positive morphostructure is
identified which may be regarded as an element of the Surt
arch (Вапцаров, Дилинска, 1980). The crestal parts of these
first-order morphodomes feature a hypsometric level of over
900 m. Their low peripheral parts around the border with the
Boundary morphostructures
In most cases, the boundary between Momchilgrad Depression
and the surrounding Central Rhodepes, Kessibir, Byala Reka,
ГОДИШНИК на Минно-геоложкия университет “Св. Иван Рилски”, том 47 (2004), свитък I, ГЕОЛОГИЯ И ГЕОФИЗИКА
70
and Popovo morphostructures is traced by well-pronounced
first-order morpholineaments. The eastern margin of the
Depression is well outlined by a system of NNE
morpholineaments inheriting the Avren-Madzharovo fault
bundle. The southern margin is marked by a system of ENE,
less commonly WNW first-order morpholineaments along
which the valleys of the Kessibir river, the upper part of the
Geogiev V. et al. MORPHOSTRUCTURES IN MOMCHILCRAD …
Vurbitsa river and other valleys are formed. The western
margin of the Depression is also well outlined by fault systems
of different orientation. The northern boundary of the
Momchilgrad Depression with its relatively slightly elevated
Kurdzhali block is traced by morpholineaments of WNW and
ENE trend. Along these, the valley of the Arda river is formed.
Fig. 2. Aerophototectonic map. 1 – lineaments; positive (2) and negative (3) ring structures; 4 – neck; 5-9 – same as in Fig .1
negative structure within the Momchilgrad Depression. The
northern margin of the Depression, the Kurdhali block, features
a similar pattern.
There are also a number of higher-order positive
morphostructures in the Depression, which inherit various
paleo-volcanic structures. The volcanic forms imprinted in the
relief show up as strongly elevated inverse forms against the
background of the structural depressions filled with
Paleogene, Neogene, and Plio-Pleistocene sediments.
On aerial photographs and on the tectonoisohypse map,
volcanic cones are usually well marked in the relief as positive
ring morphostructures. Of the volcanic cones from the
Dambala group, the relatively isolated volcanic edifices of
Zvezdel and the Iran Tepe volcanoes are best outlined. They
form positive, relatively isometric morphostructures marked by
the ring form of the tectonoisohypses and the centrifugal
configuration of the river-gorge network. The periphery of their
volcanic cones is well marked also by the arch-like
When the geologic boundary between the Depression and
the surrounding arches is not determined by faults, but by
transgressions, the morphostructural boundary is marked by
knee-like bendings of the tectonoisohypses and by abrupt
change in their values. In this way, the western boundary of the
Depression SW of the town of Kurdzhali is outlined.
Morphostructures of the Momchilgrad
Depression
The Momchilgrad Depression is well outlined as a first-order
negative morphostructure against the surrounding
morphoarches featuring a high and strongly segmented relief.
The areas, which are built-up of Paleogene sediments and
pyroclastic rocks, show a relatively smooth and lesssegmented low relief (400-600 m). Such is the situation within
the area of the Dzhebel depression constituting a second-order
ГОДИШНИК на Минно-геоложкия университет “Св. Иван Рилски”, том 47 (2004), свитък I, ГЕОЛОГИЯ И ГЕОФИЗИКА
71
Geogiev V. et al. MORPHOSTRUCTURES IN MOMCHILCRAD …
configuration of the Vurbitsa and Krumovitsa rivers and by a
part of their tributaries.
The Iran Tepe stratovolcano is imprinted in the relief as an
asymmetric ring morphostructure with steep eastern and
southern slopes and with longer and more shallow-dipping
western and northern slopes. Along its periphery, some
parasitic volcanoes project as truncated dome-like peaks.
The Zvezdel volcano features a complex orographic plan. A
central cone-like core shows up in the relief around the Strumni
Rid peak as well as a peripheral frame, built-up of long,
arcuate asymmetric hills. It is morphologically emphasized by
the radially developed river-gorge network, too. According to
Vaptsarov (1983), it constitutes an inner caldera edifice, which
was formed during the final development stages of the Zvezdel
caldera. In the geological context, no data pointing to an
existing caldera structure within the Zvezdel volcano are
available. The peripheral arch-like hill is a result of fault
deformations of the Zvezdel volcano, however preserving
some fragments from the periphery of its volcanic cone.
Fig. 3. Morphostructural map. 1 – morpholineaments; 2 – tectonoisohypses; 3 – neck; 4-8 – same as in Fig.1
extrusions of the Perperek trachyrhyolite complex are
emplaced mainly along the Hissarya magma-conducting zone.
In the inner parts of this first-order positive morphostructure,
a negative ring morphostructure is outlined. Spatially, it
coincides with the Nanovitsa caldera, nevertheless featuring
much greater dimensions while nearly touching the tops of the
surrounding volcanic cones. This negative structure should be
considered as an erosion caldera (Vaptsarov, 1983).
The actuate peripheral ridge is built-up of acid lavas and
pyroclastics, forming imprinted in the relief volcanic vents and
lava flows. They form well-expressed lava plateaus with steep
to vertical slopes. The inner caldera depression has circular
form. It is drained by the valley of the Bouyukdere river (which
forms an epigenetic defile crossing the caldera’s actuate ridge)
In the confines of the Zvezdel volcano, some second-order
ring structures can be also deciphered, which in most cases
coincide with parasitic volcanic cones, confirmed as well by
geologic data. The most typical one is the parasitic volcanic
cone along the northern slope of Zvezdel volcano, built-up by
the Momchilgrad trachydacite complex.
The Dambaluk, Bivolyane, and Sveti Iliya volcano form a joint
first-order positive ring morphostructure (the Ravena one). In
its confines, only individual fragments of the volcanic cones of
the near-by volcanoes constituting it have been deciphered.
However, their centers are well marked by their late acid
phases which are characterized by light phototone and high
relief. The southern part of this first-order structure is deformed
by the Zvezdel volcano. Along its northern periphery, the
ГОДИШНИК на Минно-геоложкия университет “Св. Иван Рилски”, том 47 (2004), свитък I, ГЕОЛОГИЯ И ГЕОФИЗИКА
72
Geogiev V. et al. MORPHOSTRUCTURES IN MOMCHILCRAD …
3. The boundary between the Momchilgrad Depression
and the surrounding morphoarches is marked in most cases by
well manifested first-order morpholineaments.
4. Volcanic structures are usually well expressed in the
modern relief as higher-order morphostructures. They are
reflected on both the aerophototectonic and the
morphostructural map. Two types of ring volcanic
morphostructures are outlined:
™ Positive, relatively isometric morphostructures with
centrifugal orientation of the river-gorge network, which inherit
volcanic cones and extrusives. The larger volcanic cones are
also well marked by the arcuate configuration of the river beds
along their periphery.
™ Negative, relatively isometric morphostructures with
centrifugal orientation of the river-gorge network, which mark
caldera edifices.
5. The use of remote sensing methods and the
potentialities of modern technologies provide for more detailed
deciphering and more correct interpretation of the boundaries
of the individual morphostructures and their spatial
relationships.
and its radial tributaries. In the inner parts of the erosion
caldera, the genuine Nanovitsa caldera with its modern
dimensions is deciphered as an inverse higher-order positive
ring morphostructure.
In the southwestern part of the Depression, the Dzhebel
negative form is well outlined, which is filled with Oligocene
sediments.
In the NE part of the studied area, part of the positive
morphostructure of the Madzharovo volcano is deciphered.
Transform morphostructures
Several inner or transit morpholineaments are observed. Along
the lower part of the Vurbitsa river, a first-order lineament with
meridional orientation can be traced. It separates the Dzhebel
depression and the NE fragment of the Central Rhodopes
dome (to the east) from the volcanic edifices (to the west). In
the eastern part of the studied region, an area of ENE oriented
morpholineaments is outlined. They can be identified in both
the Kessibir morphoarch, as well as in the inner part of the
Momchilgrad
Depression,
including
the
positive
morphostructure of the Iran Tepe volcano. Another
morpholineament system can be traced from the Kurdzhali
block and the Ravena morphostructure in the NW part of the
studied area up to the Byala Reka dome to the SE. In the SE
periphery of the Momchilgrad Depression, these lineaments
mark the Loudetino graben, wedged in-between the Kessibir
and the Byala Reka dome.
References
Georgiev, V. 2004. Late alpine tectonics and magmatism in
Eastern Rhodopes.- C. R. Acad. bulg. Sci. (in press).
Georgiev, V., P. Milovanov. 2003. Magmatic complexes in the
Momchilgrad depresion (Eastern Rhodopes).- Annual of
the University of Mining ahd Geology “St. Ivan Rilski” vol.
46, p. 1, 37-42.
Ivanov, Z., Central Rhodopes: Regional seology.- Guide,
ABCD-GEODE, Bulgaria, 2000, 1-4;
Вапцаров, И., Т. Дилинска. 1980. Морфотектонски
проблеми в Родопския масив.- Пробл. на геогр., 3, 5368.
Вапцаров, И. 1983. Вулканические кальдры оседания и их
отражение в рельефе горного хребета Стрымни-рид
(Восточные Родопы).- Докл. БАН, 36, 10,1327-1330.
Кац, Я., А. Тевелев, А. Полетаев, 1988, Основы
космической геологии. Москва, Недра. 126 с.
Спиридонов, Х., Г. Желев. 1999. Геолого-геоморфоложко
дешифриране на вулканогенни структури с помощта на
космически снимки.- Пробл. на геогр., 1-2, 89-95.
Conclusions
1. The first-order tectonic structures of the metamorphic
basement (Central Rhodopes, Byala Reka, and Kessibir core
complexes) are well expressed on the modern
morphostructural plan. They form morphoarches which feature
a high and strongly segmented relief.
2. The Momchilgrad Depression is outlined as a firstorder negative morphostructure against the background of the
surrounding morphoarches. The regions built-up of Paleogene
sediments and pyroclastic rocks feature a relatively smooth
and less segmented low relief.
Препоръчана за публикуване от
катедра “Геология и палеонтология”, ГПФ
ГОДИШНИК на Минно-геоложкия университет “Св. Иван Рилски”, том 47 (2004), свитък I, ГЕОЛОГИЯ И ГЕОФИЗИКА
73